It is well known that a flexible substrate, for example, is folded along a folding line and is positioned in a limited space in a case to provide a circuit or wiring. For example, JP 09-266368 A discloses a known three-dimensional circuit substrate obtained by forming a copper foil into a three-dimensional shape in advance, and molding the copper foil and a prepreg sheet with a molding die in a hot-press manner.
Since known flexible substrates are generally two-dimensional flat sheets, the known flexible substrate can form a folded flat sheet, but a circuit or wiring cannot be formed so as to cover faces spreading in three dimensions corresponding to length, width, and height at a corner of a three-dimensional object for example. The same applies to the known three-dimensional circuit substrate of the prior art, where a copper foil disposed on a two-dimensional plane is folded along a folding line on this plane. For example, even if a projection, for example, can be formed on the copper foil according to the technique of prior art, there is a possibility that, when the copper foil is hot-pressed together with the prepreg sheet having a shape corresponding to this copper foil, a crease or a distortion might occur in the copper foil or the copper foil might be cut in the middle.